Effect of Gas Holdup on CO2 Biofixation by Spirulina sp. in the 20-liter Airlift Bioreactor

Abstract The rise of CO2 concentration in the Earth is a major environmental problem, which cause global warming. To solve this issue, several methods have been applied, but among these solutions using microalgae is an eco-friendly and cost-effective way of reducing carbon dioxide, as they can efficiently sequestrate CO2 and produce biomass as valuable products. In this study, hydrodynamic parameters, bubble sizes and carbon dioxide uptake were investigated in an airlift bioreactor. Experiments were studied at two different superficial gas velocities (0.185 and 0.524 cm/s) for Spirulina sp. microalgae into a 20-liter airlift bioreactor to find out the amount of carbon dioxide sequestration and cyanobacterial biomass. The highest efficiency of carbon dioxide removal and maximum dry weight of Spirulina sp. were achieved 55.48% and 0.86 g/L respectively at 5% CO2 (v/v) and superficial velocity of 0.185 cm/s. This experiment was conducted in 7 days, light intensity (2600 lux/m2), temperature (30\(\pm\)2 °C) and a light-dark cycle (12–12), which all were constant. The hydrodynamic parameters studied by Spirulina sp. demonstrated a capability of CO2 sequestration in this airlift photobioreactor.